A new blood oxygenator which comes presterilized and assembled has been used in open-heart surgery. Cooling and rewarming of the patient is efficiently maintained. Blood-flow rates exceeding 5 liters/min are easily managed by the oxygenator with an oxygenating gas to blood ratio of 2:1 to 4:1. The oxygenator functions with varying priming volumes as determined by the patient's size. Total priming of the apparatus is achieved with water electrolyte solutions. Successful clinical perfusions have lasted over 3 1/2 hours with every indication that appreciably longer perfusions would be possible. Perfusions with this apparatus are capable of maintaining normal metabolic states for prolonged periods. The total inhospital blood utilization including operating room and postoperative needs by these patients has averaged 4 liters.